using System;

public class Program

{

    public static void Main()

    {

        var stringToCheck = "hi there";

        Console.WriteLine("Checksum for " + stringToCheck + ": " + CalcChecksum(stringToCheck, stringToCheck.Length));

    }

    static int CalcChecksum(string packet, int packetLength)

    {

        char checksum = (char)0;

        for (int i = 0; i < packetLength; i++)

        {

            checksum ^= packet[i];

        }

        return checksum;

    }

}